When even researchers seem conflicted about exercise subjects ranging from the amount of time we're supposed to dedicate to exercise to the proper time for a workout, it can be tough to feel motivated enough to get moving.

Because there's so much conflicting advice about health and fitness out there, we've outlined the biggest workout myths and misconceptions and countered them (where possible) with the truth. Use this as a guide to get fit in the most efficient way possible.

Myth: Exercise doesn't help counter the negative effects of aging.

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Truth: Regular exercise has key benefits for the brain and body that include helping to counteract some of the negative effects of aging.

Researchers behind a study published this summer in the Journal of the American Heart Association found that older people who spent less time sitting and more time moving had fewer signs of encroaching heart disease as measured by key markers of damage in the blood.

The scientists had 1,600 British volunteers ages 60 to 64 wear heart-rate sensors for five days. They analyzed the participants' activity levels and compared them with indicators of heart disease such as cholesterol precursors and a substance called interleukin-6. Overall, the participants with more activity had lower levels of all the negative biomarkers.

"It's important to replace time spent sedentary with any intensity level of activity," said Ahmed Elhakeem, a professor of epidemiology at England's University of Bristol who led the study.

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Myth: A sluggish metabolism is the main reason you gain weight as you age.

Myth: The best time to work out is first thing in the morning.

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Truth: The best time for a workout is whatever time allows you to exercise most consistently. Ideally, you want to make physical fitness a daily habit, so if late-night trips to the gym are your thing, stick with it. If you prefer a morning run, do that instead.

Don't have a preference? Some research suggests that working out first thing in the morning might help speed weight loss by priming the body to burn more fat throughout the day.

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Myth: Weightlifting turns fat into muscle.

Physiologically speaking, they're two different tissues. Adipose (fatty) tissue is found under the skin, sandwiched between muscles, and around internal organs like the heart. Muscle tissue — which can be further broken down into three main types — is found throughout the body.

Weight training helps to build up the muscle tissue in and around any fat tissue. The best way to reduce fat tissue is to eat a diet that incorporates vegetables, whole grains, lean proteins, and healthy fats like those found in olive oil and fish.

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Myth: Puzzles and games are great workouts for your brain.

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Truth: Plain old physical exercise seems to be better for brain health than any type of mental puzzle available, according to a wealth of research. A spate of recent studies suggests that aerobic exercise— any kind of activity that raises your heart rate and gets you moving and sweating for a sustained period — has a significant, overwhelmingly beneficial effect on the brain.

When it comes to boosting your mood, improving your memory, and protecting your brain against age-related cognitive decline, exercise may be as close to a wonder drug as we'll get.

"Sit-ups or crunches strengthen just a few muscle groups," the authors of the Harvard Healthbeat newsletter said. "Through dynamic patterns of movement, a good core workout helps strengthen the entire set of core muscles you use every day."

Myth: It takes at least a couple of weeks to get "out of shape."

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Truth: For most people, muscle tissue can start to break down within a week without regular exercise.

"If you stop training, you actually do get noticeable deconditioning, or the beginnings of deconditioning, with as little as seven days of complete rest," said Shawn Arent, the director of the Center for Health and Human Performance at Rutgers University. "It very much is an issue of use it or lose it."

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Myth: Running a marathon is the ideal way to get fit.

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Truth: You can get many of the benefits of long-distance running without ever passing the five-mile mark.

Not ready to conquer a marathon? No problem. Running fast and hard for just five to 10 minutes a day can provide some of the same health outcomes as running for hours. In fact, people who run for less than an hour a week — as long as they get in those few minutes each day — see similar heart-health benefits compared with those who run more than three hours a week.

Myth: Keeping a food diary is a reliable way of monitoring and controlling what you eat.

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Truth: Even when we're making an effort to be conscious about what we're putting into our bodies and how active we're being, we often give ourselves more credit than we deserve.

"People tend to overestimate their physical activity and underestimate how much food they eat," Stanforth said. "They consistently think they've worked out more and consistently think they've eaten less."

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Myth: Sports drinks are the best way to rehydrate after a workout.

Instead, experts recommend refueling with plain old water and a high-protein snack, since studies suggest protein helps recondition muscles after a workout. (Because the contents of supplements like protein powders can be largely unregulated, however, your best bet is to eat real protein-packed food.)

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Myth: Your body mass index is an accurate way to size up your overall health.

For the latest study, researchers looked at data on physical activity and death rates from national surveys of more than 4,800 adults and found that people who clocked roughly 30 minutes a day of exercise were significantly less likely to die from any cause than people who got none. The type of exercise mattered less than the simple fact that they were regularly moving.

"The key message based on the results presented is that total physical activity (i.e., of any bout duration) provides important health benefits," the authors said.